It may be desirable to utilize recycled elastomer in new elastomeric compositions. When recycling elastomers, it is generally known to decrease the size of the elastomeric material to be recycled to very small size particles. Such particles have been discovered to be mechanically easier to mix into new elastomeric compositions and provide compositions having improved physical properties over compositions comprising particles of larger size. A wide range of elastomeric products may be recycled. Such materials include natural or synthetic rubber scrap and automotive tire scrap.
Various methods have been suggested in the prior art for reducing the size of elastomeric particles as part of a recycling process, including cryogenic cracking of the particles and various grinding or chopping methods.
A particularly advantageous method for reducing the size of elastomeric particles is a wet-grinding process, where a slurry of liquid, usually water, containing elastomeric material is passed through grinding stones. The liquid helps keep the elastomeric material cool during the grinding process and helps prevent the material from thermally degrading. Cryogenic cracking can also control the amount of thermal degradation in the elastomeric material. However this process is typically more costly than the wet-grinding method.
Even though methods exist for reducing the size of elastomeric particles, the use of recycled vulcanized elastomeric particles in products requiring resistance to oxidation and ozone, e.g., tire sidewalls, has been limited due to the lower oxidation and ozone resistance in the products produced using the recycled vulcanized elastomeric particles. It is believed that oxidation and ozone resistance are lowered since the elastomeric material to be recycled has already expended most of the antidegradant it contained to resist oxidation and ozonation. Thus, the recycled elastomeric particles provide locations for oxidation and ozonation to occur. Moreover, simply adding more antidegradant to a new elastomeric composition containing recycled elastomeric particles does not adequately improve the oxidation and ozone resistance.
Accordingly, an elastomeric particle has been discovered that provides improved oxidation and ozone resistance over the elastomeric particles of the prior art. Methods for producing the particles have also been discovered.
As used herein, the term “antidegradant” includes both antioxidants and antiozonants.
As used herein, the terms “particle(s)” and “piece(s)” are used interchangeably, and represent portions or fragments of various sizes.